Solar Thermochemical SpliQng of H 2 O and CO 2 using Metal Oxide Based Redox Cycles

Transcription

1 Solar Thermochemical SpliQng of H 2 O and CO 2 using Metal Oxide Based Redox Cycles Jonathan Scheffe, Aldo Steinfeld Department of Mechanical and Process Engineering, ETH Zurich, Switzerland Sustainable Fuels from Renewable Energies, Potsdam, November 19-20, 2013 IASS Workshop 11/28/13 1

2 Paths to Solar Fuel ProducWon Energy Input Process Photobiological H 2 O CO 2 H 2 O/ CO 2 Photons (hν) Photoelectrochemical PhotocatalyWc Photosynthesis H 2 CO + + CO 2 H 2 O Electricity (e - ) Thermal Energy (U internal = f(t)) Electrolysis Thermochemical Solar thermal processes inherently operate at high temperatures and u4lize the en4re solar spectrum, and as such provide a thermodynamically favorable path to solar fuels produc4on. CO+H 2 CO+H 2 CO+H 2 SyntheWc Fuels via Fischer- Tropsch MethanaWon IASS Workshop 11/28/13 2

3 Thermochemical Fuel ProducWon Solar ConcentraWon Heliostat Field H 2 O/CO 2 H 2 O purificawon/ CO 2 sequestrawon Receiver/Reactor Q solar = IC C=A field /A receiver Q solar Chemical Reactor/Receiver O 2 Liquid Fuels (diesel, kerosene, etc.) Cracking FT Reactor Δ ( n+ ) 2 + n n 2n+ 2 + n H CO C H H O Compression H 2 /CO IASS Workshop 11/28/13 3

4 Solar Thermochemical Efficiency ηmax = ηcarnotηabs L η carnot = 1 T T H 4 H Qre-rad σt η abs = 1 = 1 Q IC solar Carnot ,000 η Carnot η abs ,000 20,000 10, IASS Workshop 11/28/13 4 Fletcher and Moen, Science 197, , 1977.

5 Thermochemical DissociaWon of H 2 O/CO 2 H 2 O/CO 2 Q solar Two- Step Direct DissociaWon Redox Cycle +Δ 1) MO HChemical 2 O MO H 2 Reactor + 1- δ 0.5O + δ/2o Δ 2) MOCO 1- δ 2 + δhco 2 O + 0.5O MO 2 + δh 2 O 2 Direct DissociaWon Two- Step Redox Cycle High temperatures (> 2500 K) Rapid quenching or separawon of products H 2 /CO Lower temperatures (>1673 K) Inherent separawon of product gases IASS Workshop 11/28/13 5

6 Thermochemical Efficiency of H 2 O/CO 2 DissociaWon Q solar MO T H Δh red MO 1- δ δh 2 MO T L MO 1- δ HeaWng Solid Reactants + Endothermic ReducWon + HeaWng Fluid Reactants = = = T T H L c Δh p,ox Δhredδ dt HO 2 298K TL δ Qin = Qsolarη abs δ/2o 2 δh 2 O η = solar-to-fuel Q δ HHV solar + E H 2 penalty IASS Workshop 11/28/13 6

7 Common Metal Oxide Intermediates Ferrites (Fe 3+ /Fe 2+ ) Fe- based oxides of the form M x Fe 3- x O 4, M = Co, Ni, Zn DeposiWon on or incorporawon with inert materials (YSZ or ZrO 2 ) ZnO/Zn Higher O 2 uwlizawon results in high theorewcal efficiencies Zn(g)/O 2 (g) mixture must be quenched rapidly Ceria (CeO 2- δ ) Lower capacity (nonstoichiometric reducwon, δ), but thermodynamics and kinewcs can be altered through doping (i.e. Zr 4+, Hf 4+ ) Morphologically and crystallographically stable Perovskites (ABO 3- δ ) Nonstoichiometric reducwon/oxidawon similar to ceria Largely unexplored, but promising class of materials IASS Workshop 11/28/13 7

8 Ceria Thermodynamics δ, in CeO 2- δ, increases with temperature and decreasing p O 2 ' 1 2CeCe + OO VO + 2CeCe + O2 g 2 ( ) Q solar CeO2 δ i ( δ δ ) f i 2 CeO2 δ H i Δ g =Δh TΔs O O O Δ g = RT ln p O ln p 1 2 O 2 O ΔhO 1 ΔsO = + 2 RT 2 R δ = p 5 O = 10 atm 2 const T H Δh red CeO2 δ f T L CeO2 δ f p 1 O = 10 atm 2 ( δ δ ) f 2 i O 2 ( δ δ ) HO f i 2 Panlener, R. J. et al., Journal of Physics and Chemistry of Solids 1975, 36 (11), Scheffe, J. R., Steinfeld, A., Energy & Fuels 2012, 26 (3), IASS Workshop 11/28/13 8

9 Ceria Thermodynamics δf,th Q solar ( δ δ ) H f i 2 From knowledge of Δg o and K w, H 2 yields can be determined Δ = = g 2 O RT ln po RT ln K 2 w p p 1 HO 2 H 2 CeO2 δ T H Δh red CeO2 δ i f CeO2 δ T L CeO2 δ i f ( δ δ ) f 2 i O 2 ( δ δ ) HO f i 2 Panlener, R. J. et al., Journal of Physics and Chemistry of Solids 1975, 36 (11), Scheffe, J. R., Steinfeld, A., Energy & Fuels 2012, 26 (3), IASS Workshop 11/28/13 9

10 Ceria Thermodynamics Q solar ( δ δ ) H f i 2 p HO 2 CeO2 δ i CeO2 δ i 4 p HO 2 T H Δh red CeO2 δ f T L CeO2 δ f ( δ δ ) f 2 i O 2 ( δ δ ) HO f i 2 Panlener, R. J. et al., Journal of Physics and Chemistry of Solids 1975, 36 (11), Scheffe, J. R., Steinfeld, A., Energy & Fuels 2012, 26 (3), IASS Workshop 11/28/13 10

11 Ceria Thermodynamics δf,th Q solar ( δ δ ) H f i 2 ( δ δ ) H f i 2 CeO2 δ i CeO2 δ i T H Δh red T L δ,t i L CeO2 δ f CeO2 δ f T L ( δ δ ) f 2 i O 2 ( δ δ ) HO f i 2 Panlener, R. J. et al., Journal of Physics and Chemistry of Solids 1975, 36 (11), Scheffe, J. R., Steinfeld, A., Energy & Fuels 2012, 26 (3), IASS Workshop 11/28/13 11

12 Ceria- Based Solar Reactor 2010 First operable and cyclable solar reactor demonstrawng complete redox cycle Average efficiencies reported ~ 0.6% Room for opwmizawon in several areas Structural opwmizawon Reactor opwmizawon Material opwmizawon Heat recuperawon Chueh, W. C, Steinfeld, A. et al., Science 2010, 330 (6012), IASS Workshop 11/28/13 12

13 European Union Project SOLAR- JET EU FP7- AeronauWcs and Air TransportaWon DemonstraWon and opwmizawon of carbon- neutral solar kerosene producwon from CO 2 and H 2 O DuraWon 4 years (June 2011) EC funding 2.2 mil EUR 20 people involved Industrial advisory board Luqhansa EADS Deutschland MTU Aero Engines GmbH IATA (InternaWonal Air TransportaWon AssociaWon) IASS Workshop 11/28/13 13

14 Solar Reactor Prototype Al 2 O 3 insulawon CeO 2 structure Reactor Reactor Front (water- cooled) OxidaWon Thermal ReducWon: Ce O 2 δ +δ H 2 ΔH CeO 2 δ O CeO 2 + δ/2 +δ H 2 O 2 Ce O 2 δ +δ CO 2 CeO 2 +δco Syngas (H 2 / CO) D 20cm Outlet Inlet O 2 CO C C O 2 H2 H 2 O 2 Quartz Window Concentrated Solar RadiaWon Inconel Shell H 20cm Purge H 2 O / Gas CO 2 (Ar) Furler, P. et al, Energy & Environmental Science 2012, 5, Furler, P. et al., Energy & Fuels 2012, 26 (11), Chueh, W. C, Steinfeld, A. et al., Science 2010, 330 (6012), IASS Workshop 11/28/13 14

15 Experimental Setup Furler, P. et al, Energy & Environmental Science 2012, 5, IASS Workshop 11/28/13 15

16 Typical CO 2 DissociaWon Results Experimental Conditions Reduction Oxidation Gas Flow: 2 l min -1 Ar 3 l min -1 CO 2(g) Ceria Structure: Ceria RPC: 1416 g 0.6 reduction oxidation 2000 Rate (ml min -1 g -1 CeO 2 ) T ceria O 2 : 2.3 ml g -1 CO: 4.7 ml g l 6.61 l Temperature ( C) O 2 / fuel evoluwon increases with power input No gas phase hydrocarbons detected No deposiwons of carbon inside the reactor => total selecwvity towards syngas producwon Stoichiometric fuel producwon (O 2 :CO = 2) Time (min) IASS Workshop 11/28/13 16 Furler, P. et al., Energy & Fuels 2012, 26 (11),

17 Rate [ml min -1 g -1 CeO 2 ] Rate [ml min -1 ] Comparison: Felt vs. RPC CeO 2 felt O 2 Evolution O 2 Felt : 2.66 ml g -1 O 2 RPC : 2.83 ml g -1 O 2 Felt : 0.24 l O 2 RPC : 4.00 l O 2 evolution CeO 2 felt O 2 evolution CeO 2 RPC Time [min] Heating Rate CeO2 felt Heating Rate CeO2 RPC O2 evolution CeO2 felt O2 evolution CeO2 RPC Rate [ml min -1 g -1 CeO 2 ] CeO 2 RPC x μm 1.5 x μm Rate [ml min -1 ] Furler, P. et al., Energy & Fuels 2012, 26 (11), CO Evolution CO evolution CeO 2 felt CO evolution CeO 2 RPC CO Felt : 5.39 ml g -1 CO RPC : 5.86 ml g Time [min] CO Felt : 0.49 l CO RPC : 8.27 l Experimental Conditions Reduction Oxidation Power Input: 3.6 kw 0.7 kw Gas Flow: 2 l min -1 Ar 3 l min -1 CO 2(g) Ceria Structure: Ceria RPC: 1416 g, Ceria felt; 90 g Total O 2 / CO evoluwon per gram of CeO 2 comparable Felt shows considerably higher CO rates - higher surface area x μm x μm But: overall 17 Wmes higher fuel producwon per cycle with RPC structure Furler, P. et al, Energy & Environmental Science 2012, 5, IASS Workshop 11/28/13 17

18 Solar- to- Fuel Conversion Efficiency solar-to-fuel (%) η average = Δ H fuel r fuel dt / P solar dt + E inert r inert dt η peak = 2 r oxygen Δ H fuel / P solar + r inert E inert t Reduction T Ceria P solar (kw) h solar-to-fuel Reduction step duration (min) Nominal reactor temperature ( C) Δ H fuel =high heating value of r fuel =molar fuel production r oxygen =molar O 2 release ra r inert =flow rate of inert gas E inert =energy for separation of inert gas from air (20 kj mo P solar =radiative power input Efficiency increases with power input ReducWon Wme decreases with power input η average RPC = 1.73 % η average Felt = 0.15 % η peak Felt = 0.31 % IASS Workshop 11/28/13 18 Furler, P. et al., Energy & Fuels 2012, 26 (11),

19 Structural Improvements of Ceria x μm Two important traits of structure 1) Heat transfer limited during reducwon 2) KineWcally limited during oxidawon Furler, P. et al, Energy & Environmental Science 2012, 5, Furler, P. et al., Energy & Fuels 2012, 26 (11), Marxer, D., Master Thesis, ETH Zurich IASS Workshop 11/28/13 19

20 Single- scale vs. MulW- scale RPC 250 µm 250 µm Marxer, D., Master Thesis, ETH Zurich IASS Workshop 11/28/13 20

21 CO 2 SpliQng Cycles in TGA Experimental conditions Reduction Oxidation Gas concentration: po 2 : 1.8*10-4 atm pco 2 : atm Nonstoichiometry δ: δi = δf = reduction oxidation T Ceria 1600 Weight (%) vol% pore former 0 vol% pore former Temperature ( C) Time (min) OxidaWon Wme decreased from 28min to 3min (to reach 90% re- oxidawon) IASS Workshop 11/28/13 21

22 CO 2 SpliQng Cycles in TGA 0.12 Rate (ml min -1 g -1 CeO 2 ) Isolated strut pores mean reaction rate surface area Transition zone Interconnected strut pore network d i = d f = [CO 2 ] = 38.5 Vol-% T = 1000 C Specific surface area (m 2 g -1 ) Pore former (Vol-%) IASS Workshop 11/28/13 22 Marxer, D., Master Thesis, ETH Zurich 2013.

23 SEM micrographs Interconnected pore-network Only closed pores Transition zone IASS Workshop 11/28/13 23 Marxer, D., Master Thesis, ETH Zurich 2013.

24 Structural and Reactor Improvements Determine of effect heat and mass Implement reacwve structure into reactor transfer properwes on macro and model micro scales OpWmize reacwve structure and reactor DeterminaWon of kinewc parameters geometry to allow opwmal Material inveswgawons Heat and mass transfer ReacWon rates IASS Workshop 11/28/13 24

25 Oxygen Diffusion Rates RelaxaWon Studies Gas Chromatograph δ i T =1723 K Insulation p O high = Heating Element Thermocouple CeO 2 Sample Crucible Sample Carrier Radiation Shield Inlet: Ar/O 2 mixture p O low = δ f 2 3 Ackermann, S., Master Thesis, ETH Zurich Purge: Ar Balance System d = 1.1 cm l = 0.72 cm ρ rel = 88.4% (,, ) C t r z t = ( D C( t, r, z) ) IASS Workshop 11/28/13 25

26 Oxygen Diffusion Rates RelaxaWon Studies Raw Data ResulWng Diffusion Coefficients atm atm IASS Workshop 11/28/13 26 Ackermann, S. Scheffe, J. R., Steinfeld, A., SubmiHed to Chemistry of Materials 2013

27 Oxygen Diffusion Rates ApplicaWon of Model RPC (middle) reducwon takes place on the order of seconds Small parwcles reducwon takes place < 1s Consistent with observawons in the solar reactor heat transfer limited IASS Workshop 11/28/13 27 Ackermann, S. Scheffe, J. R., Steinfeld, A., SubmiHed to Chemistry of Materials 2013

28 Material InvesWgaWon: Doped Ceria and Perovskites Ceria dopants (ZrO 2, Sm 2 O 3, HfO 2 ) and other nonstoichiometric metal oxides (perovskites, ABO 3- δ ) are capable of increasing reducwon extents at a given T and p O2 ReducWon extent η solar-to-fuel They can provide the ability to operate the cycle at lower reducwon temperatures But, if a material is more easily reduced it is generally more difficult to reoxidize it with H 2 O/CO 2 IASS Workshop 11/28/13 28

29 Material InvesWgaWon: Doped Ceria and Perovskites IASS Workshop 11/28/13 29 Scheffe, J. R., et al. In Press JPCC 2013

30 La 0.65 Sr 0.35 MnO 3 (LSM35) ReducWon Extents > Ceria IASS Workshop 11/28/13 30 Scheffe, J.R. et al., Energy and Fuels 2013.

31 LSM30/LSM40 OxidaWon Extents < Ceria IASS Workshop 11/28/13 31 Scheffe, J.R. et al., Energy and Fuels 2013.

32 Total CO Yields with LSM35 > Ceria IASS Workshop 11/28/13 32 Scheffe, J.R. et al., Energy and Fuels 2013.

33 Conclusions and Outlook Metal oxide based redox cycles are shown to be an azracwve and feasible concept for the producwon of solar fuels. ReducWon rates are primarily driven by heat transfer, at least for the ceria RPC`s currently being uwlized. OxidaWon rates are likely limited by the available reacwve surface area of the RPC. CharacterizaWon of ceria heat and mass transfer properwes and chemical kinewcs is ongoing. UlWmately these properwes will be opwmized in series with a reactor model to maximize solar to fuel efficiencies. Because of the relawvely low reducwon extents of ceria, heat recuperawon is necessary for further opwmizing this process. IASS Workshop 11/28/13 33

34 Conclusions and Outlook Doped ceria, especially Hf doped ceria, and LSM perovskites appear to be promising alternawves to ceria and offer the potenwal to increase fuel yields. However, further understanding of their thermodynamic, kinewc and morphological properwes is needed. Perovskites are another class of nonstoichiometric materials which have largely been expolored, but preliminary studies incidate they are promising. The range of perovskites formulawons to be explored is enormous as A and B site doping in ABO 3 lead to very different thermodynamic and kinewc properwes. IASS Workshop 11/28/13 34

35 Acknowledgments Prof. Aldo Steinfeld, Ph.D. Philipp Furler Simon Ackermann Daniel Marxer David Weibel Michael Welte Prof. Greta Patzke, Ph.D. Roger Jacot Dr. Zoran Jovanovic EU- SOLAR- JET - European Commission under contract No Swiss Competence Center for Energy and Mobility European Union ERC Advanced Grant (SUNFUELS n ) PRE Laboratory IASS Workshop 11/28/13 35